The invention relates to a tachometer apparatus and methodology for determining the velocity of a motor as applied to a vehicle steering system.
Speed sensors, or detectors of various types are well known in the art. In recent years the application of speed detection to motor control functions has stimulated demands on the sophistication of those sensors. Rotational speed sensors are commonly configured in the same manner as an electric machine, for example, a coil is placed in proximity to rotating magnets whereby the magnetic field induces a voltage on the passing coil in accordance with Faraday""s Law. The rotating permanent magnets induce a voltage on the coil and ultimately a voltage whose frequency and magnitude are proportional to the rotational speed of the passing magnets.
Many of the tachometers that are currently available in the art exhibit a trade off between capabilities and cost. Those with sufficient resolution and accuracy are often very expensive and perhaps cost prohibitive for mass production applications. Those that are inexpensive enough to be considered for such applications are commonly inaccurate or provide insufficient resolution or bandwidth for the application.
Thus, there is a need, in the art for a low cost robust tachometer that provides sufficient accuracy and resolution for motor control applications and yet is inexpensive enough to be cost effective in mass production.
The above-identified drawbacks of the prior art are alleviated by the method described in the invention.
A method and apparatus for determining the velocity of a rotating device is described herein. The apparatus includes sets of sense magnets affixed to a rotating shaft of a rotating device and a circuit assembly, which interact to form an air core electric machine. The circuit assembly includes a circuit interconnection having sense coils and sensors affixed thereto. The circuit assembly is adapted to place components thereon in close proximity to the sets of sense magnets on the rotating part.
A controller is coupled to the circuit assembly, where the controller is adapted to execute an adaptive algorithm that determines the velocity of the rotating device. The algorithm is a method of combining a derived velocity with a measured velocity from the tachometer. The algorithm includes a plurality of functions including: generating a position signal related to the rotational position of the shaft; determining a derived velocity from the position signal and then filtering it to eliminate noise; generating two or more measured tachometer velocity signals; generating a compensated velocity in response to said two measured tachometer velocity signals; and blending the compensated velocity with derived velocity to generate a blended velocity output.